This application claims the priority benefit of European patent application EP 99 116 941.8 filed on Aug. 27, 1999.
The invention relates to a method and an apparatus for dehulling oil-bearing seeds, in particular sunflower seeds. This involves separation of the husk or hull(pericarp) from the kernel (embryo) of the seeds (in the case of sunflower seeds it involves separation from the achenes).
Usually, the seeds of oil-bearing plants such as sunflower, Euphorbia lathyris and coriander are characterized in that the kernel is held together by a seed membrane which in turn is protected by a porous water-absorbing husk (pericarp). If the husks or hulls are not removed before oil extraction, they absorb considerable quantities of oil, at least 7% of their weight, thus reducing oil yield during pressing. The oil absorbed by the husk can subsequently only be recovered and extracted by means of solvents.
For some considerable time, various methods and devices have been used to remove the husks or hulls of e.g. sunflower seeds or other oil-bearing crops, such as soybeans. One frequently applied method consists of considerably accelerating the individual seeds and dehulling them by impact. In this method, the seeds impact at high speed on a solid stationary object so that their hulls or the like burst as a result of the braking force at impact. Thus rotating disks made of metal or hard plastic are used throwing the seeds against a rebound plate where they burst depending on their own hardness and the mechanical forces acting upon them. The resulting hull fragments or the like are removed by exhausters or are separated via shaking sieves.
Furthermore, modified devices for removing hulls or the like from sunflower seeds or soybeans have been proposed. The modified devices also accelerate the seeds or beans, as far as possible individually, and husk or dehull them by impact, (e.g. DE 29 16 729 A1). In conventional beaters, impact and its effect are also used for dehulling. Rubber roller husk or hull removers and devices with two rotating rubber plates have also been used with seeds being rolled under light pressure between said plates, so as to remove the husks or hulls. This requires particularly careful size grading of the seed products before the dehulling process.
Dehulled sunflower seeds for the foodstuffs industry have been produced by hydrothermally treating the seeds in steam so as to break the mechanical adhesion between the seeds and the hulls by subsequent fast drying of the superficially moistened hulls. At the same time the seed membrane is loosened and as far as possible separated from the seed (DE 32 19 421 A1). Soybeans too have been subjected to heating prior to dehulling, so as to separate the hulls from the beans and destroy the anti trypsin in the bean by contact with hot surfaces and a subsequent application of a hot gas stream (DE 35 44 387 A1).
The cited literature also mentions the usual measures for separation of the husks or hulls removed in the dehulling device, by means of separator mechanisms like sifters or corona gravity separators. Combinations using electric separators too, have been used for separating the dehulled product from the husks or hulls.
In each of the above methods and devices, the kernel is often damaged, not only by mechanical forces experienced during impact etc. but in particular also by the fact that the seed membrane which surrounds the kernel is destructed during the dehulling process. This results in the kernel losing oil during the dehulling process already and the kernel in addition coming into direct contact with atmospheric oxygen and humidity which is disadvantageous.
The present invention provides a method and apparatus for dehulling oilbearing seeds, such as sunflower seeds, in which a quantity of bulk material of the oilbearing seeds is filled into a confined space. The bulk material is subjected to agitating movement and pressure build-up within the confined space such that the oilbearing seeds are pressed and rubbed against each other and against separated hull fragments kept in the bulk material. The pressing and rubbing gently removes the hulls from the seeds.
A general objective of the present invention is to provide a method and apparatus which dehulls oil-bearing seeds, in particular sunflower seeds, while being careful with the kernel. This objective is accomplished by pressing and rubbing the seeds together to remove the hulls.
This and still other objects and advantages of the present invention will be apparent from the description which follows. In the detailed description below, preferred embodiments of the invention will be described in reference to the accompanying drawings. These embodiments do not represent the full scope of the invention. Rather the invention may be employed in other embodiments. Reference should therefore be made to the claims herein for interpreting the breadth of the invention.